Morphological variation of certain blue-green algae in culture:Scytonema stuposum (Kütz.) Born

S. stuposum has been studied in culture for its morphological variability using different media. In modified Chu 10 and Gerloff's media typical Scytonemoid condition with normal false branches and heterocysts was developed whereas in the 2 Zehnder and Gorham's media the branches became most often atypical. In Allen and Arnon's medium, on the other hand, a more or less complete suppression of heterocysts and normal false branches resulted. The taxonomic criteria for a clear-cut separation of Scytonema and Tolypothrix are shortly discussed and the importance of selecting a suitable medium for obtaining a complete morphological expression of an alga has been stressed.